Prior attempts to develop a flat panel display include gas plasma panels, electroluminescent panels, liquid crystal panels, the classic Gabor tube, and the Aiken tube. These attempts have been unsuccessful for a variety of reasons, including insufficient illumination or contrast, low resolution, excessive power consumption, insufficient reduction in tube depth, difficulties in focusing, difficulties in deflection and the complexity and cost of implementing a suitable color display.
The Aiken tube is of interest due to its achievement of a geometrically flat structure using a single, side-mounted electron gun and a matrix of vertical and horizontal deflection elements to deflect the electron beam to the picture elements on a phosphor screen, as shown for example in U.S. Pat. Nos. 2,795,731 and 2,928,014. However, the Aiken tube requires as many horizontal and vertical deflection elements and associated drivers as picture elements for resolution in the respective directions. It therefore suffers a trade-off of size, cost, and complexity against display resolution and focus. These problems make implementation of a color display particularly difficult. Moreover, the matrix arrangement of deflection elements requires that the beam be deflected sharply at right angles in the vertical and horizontal directions, thereby making deflection driving coercive and lowering the focus of the beam.
One variation of the Aiken-type flat panel display is the parallel guided beam structure developed by RCA Corporation. In the RCA flat panel display, a plurality of channels extend in parallel with a screen, and each channel has a beam guide structure which guides a respective beam along the length of the channel. The beams in all of the channels are deflected simultaneously out of the beam guides at selected points corresponding to a series of horizontal line positions. This type of display requires as many beams as picture elements desired for horizontal resolution in black and white operation and three times as many for color operation. In U.S. Pat. No. 4,028,582 of Anderson, the RCA beam guide structure is improved by providing a pair of channel deflection electrodes on opposite sides of the width of each channel which deflect the beam transversely across a line segment of picture elements, thereby allowing a higher line resolution with a reduced number of beams. However, this device still requires a plurality of separate beams, channels, and channel deflection drivers.
Conventional color CRT displays employ three separate electron guns to generate beams which are directed through a shadow mask at different angles to impinge on triads of color phosphor elements forming each picture element. The intensities of the beams are modulated by modulating the output intensities of the beam emitting guns. A relatively high range of beam intensities must be used in order to sufficiently control the downstream illumination of the color phosphor elements by the respective beams. The shadow mask has apertures dimensioned and positioned corresponding to the directions of the respective beams and positions of the color phosphor elements. The widths of the beams are made wider than the apertures, so that the beams can be collimated to the widths of the phosphor elements by the apertures of the shadow mask closer to the target. The portions of the beams which are not passed generate large amounts of heat in the shadow mask, thereby wasting energy and causing thermal stresses in the tube structure.